FIG. 5A and FIG. 5B are respectively plan views of a storm overflow chamber of a conventional combined sewer system, FIG. 6A and FIG. 6B show a state in a fine weather of the storm overflow chamber of the combined sewer system in FIG. 5A. Reference numeral 2 denotes an inflow pipe which opens on a side wall side wall forming the storm overflow chamber. Reference numeral 3 denotes an intercepting pipe which similarly opens on a side wall. Reference numeral 4 denotes an outflow pipe. Reference numeral 1 denotes a separating weir which is provided in the storm overflow chamber, separates the opening of the inflow pipe 2 and the opening of the intercepting pipe 3 from an opening of the outflow pipe 4, and is higher than the opening of the outflow pipe 4. Reference numeral 5 denotes floating debris which flow from the inflow pipe 2. FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B show states in a rainy weather of the storm overflow chamber of the combined sewer system shown in FIG. 5A.
In the conventional storm overflow chamber shown in FIG. 5A, entire waste water containing the debris 5 flows from the inflow pipe 2 into the intercepting pipe 3 in a fine weather, and then flows into a sewage treatment plant, and a pump station as shown in FIG. 6A and FIG. 6B. Rain water flows into the storm overflow chamber along with waste water in a rainy weather as shown in FIG. 7A and FIG. 7B, and if a water quantity exceeds a certain quantity, the water overflows over the separating weir 1 interposed between the inflow pipe 2 and the outflow pipe 4, and a part of the waste water containing the debris flows out to a public water body via the outflow pipe 4 as shown in FIG. 8A and FIG. 8B.
As described above, in the conventional storm overflow chamber, the inflowing floating debris 5 do not flow into the intercepting pipe 3 in a rainy weather, and flow out to the public water body via the outflow pipe 4, constituting a cause of water pollution in the public water body. One reason is a hydraulic characteristic in the rainy weather in the conventional storm overflow chamber. In the conventional storm overflow chamber, a water surface gradient is formed from the inflow pipe 2 toward the intercepting pipe 3 in a fine weather as shown in FIG. 6A and FIG. 6B, the floating debris 5 thus are entirely brought by the flow into the intercepting pipe 3. However, in a rainy weather, the intercepting pipe 3 is submerged in the water, the water surface rises in a vicinity of the inlet of the intercepting pipe 3, and the water surface gradient from the inflow pipe 2 toward the outflow pipe 3 is not formed as in the fine weather as shown in FIG. 7A and FIG. 7B in a rainy weather. In this state, the floating debris 5 do not flow into the intercepting pipe 3, and remain in the storm overflow chamber. If the quantity of the water flowing into the storm overflow chamber increases, and the water depth consequently exceeds the height of the separating weir 1 in the storm overflow chamber, the water surface gradient is formed by an overflow over the separating weir 1 from the inflow pipe 2 toward the outflow pipe 4 as shown in FIG. 8A and FIG. 8B. On this occasion, the floating debris 5 are almost entirely brought by the flow out to the public water body via the outflow pipe 4.
As means to solve this problem, it is necessary to generate a flow which facilitates the flow of the floating debris 5 into the intercepting pipe 3 in the storm overflow chamber, and it is thus necessary to improve the conventional storm overflow chamber so as to reduce the floating debris which flow out to the public water body.